The invention concerns a method for producing an iron melt, in particular a crude steel melt, using iron-containing residual smelting plant materials, and an installation for carrying out the method.
For a process of directly reducing iron ore with subsequent melting down of iron sponge and simultaneous coal gasification, it is known (AT-B-376,241) to separate particulate solids, primarily consisting of carbon in dust form, from the reduction gas formed in a fusion gasification zone and from the waste gas produced during direct reduction, to mix the separated particulate solids with binder, including with iron oxide dust, to make formed coke by hot-briquetting and subsequently to feed the formed coke back to the melting-down process.
It is disadvantageous in this case, however, that, because of the introduction of iron oxides in the fusion gasifier, reduction work has to be performed in order to reduce the iron oxide, whereby energy required for the melting-down process is taken from the said iron oxide and the process taking place in the fusion gasification zone is disrupted. Furthermore, the said hot-briquetting represents an expensive solution with regard to the investment and operating costs.
It is known from DE-A-41 23 626 to agglomerate residual smelting plant materials of mixed consistency, with the aid of binders, slag-forming constituents and reduction agents, and to introduce the agglomerates into the upper burden region of a melting unit, the preheating and drying of the agglomerates taking place in this burden region of the melting unit. The burden passes through the melting unit on the basis of the counterflow principle, it initially arriving in a reduction region, provided in the interior of the melting unit, and being subsequently melted in the lower region of the melting unit.
This known method is energy-intensive to the extent that metallic scrap or residual materials also have to pass through the reduction region of the melting unit. A particular problem here is the stability of the agglomerates, since these agglomerates are used while still in the green state, that is to say not completely dried, which in practice causes great difficulties due to disintegration, abrasion etc. When passing through the melting unit on the basis of the counterflow principle, destruction of the agglomerates caused by forces of pressure and impact can lead to a high proportion of the said agglomerates being discharged from the melting unit through the waste gas. For this reason, the method known from DE-A-41 23 626 can only be realized with difficulty in practice. Agglomerates with a high stability, which they should also have in the high temperature range, would have to be produced, which in turn is very expensive, however, and would require in particular the use of high-grade and correspondingly expensive binders.
It is known from AT-B-380,901 to convey metal-oxide-containing metallurgical dusts together with carbon-containing material through a rotary tube, to reduce them in a hot zone of the tube and to form iron sponge, and to use this iron sponge in a converter as a substitute for chill scrap. This method has proven successful in the case of metal-oxide-containing metallurgical dusts, but requires additional expenditure on apparatus and process technology to establish a reducing atmosphere. What is more, only metal-oxide-containing metallurgical dusts can be reprocessed; this method is not envisaged for the use of dusts containing high proportions of metallic iron.
A method of the type described at the beginning is likewise known from EP-A-0 623 684. In this case, a complete and energy-saving reprocessing of waste and residual materials of the metallurgical industry is successfully achieved in a method for the direct reduction of iron ore into iron sponge and melting down of the iron sponge in a coal gasification zone, it being necessary however to collect the waste or residual materials separately in groups according to their chemical composition. A first group mainly comprises iron in oxidic form, a second group iron in metallic form and a third group mainly carbon-containing materials. The first group is charged into the direct reduction zone and the second and third groups are charged directly into the fusion gasification zone, charging being preceded by carrying out thickening and granulating of the waste and residual materials occurring in the form of slurries.
In the case of this known method, it is primarily intended to feed the dusts produced in the waste gases during direct reduction or melting-down and during coal gasification back to the direct reduction or the melting-down process and coal-gasification process. This is complex to the extent that the agglomerates are in turn fed back to the same processes from which they originate. They consequently have to be heated up again there and run through these processes as it were a second time, and only subsequently can they be further processed in a downstream process, for example a process for producing steel from pig iron.
It is likewise know from U.S. Pat. No. 5,100,464 to mix residual smelting plant materials, bind them with molasses and to make briquettes in a cold-briquetting process and charge them into a converter.
A method of this type is also know from WO-A-96/34120 as well as U.S. Pat. No. Re. 30,795 and U.S. Pat. No. 4,119,455.
Furthermore, numerous methods of melting down zinc-containing metallurgical dusts are known, in which zinc-containing dusts are melted down by means of electrical energy, such as by means of plasma burners or conventional electric arcs. These methods serve for recovering the zinc, but not for producing an iron melt. These methods are known by the names xe2x80x9cMintek methodxe2x80x9d, xe2x80x9cElkem methodxe2x80x9d, xe2x80x9cIMS-Tectronics methodxe2x80x9d or xe2x80x9cDavy McKee methodxe2x80x9d.
It is generally known in the blast-furnace process, oxygen steelmaking process or in the direct reduction of iron ore into iron sponge to separate dusts occurring in the wet process from the waste gases forming during these processes, and to dry the slurries thereby formed, but the slurries are usually subsequently landfilled for reasons of low cost. This has been accepted in the past, since these slurries (as dry substance) only make up approximately 1.5% by weight of the amount of steel produced. However, with increasing environmental awareness, there is increasingly a requirement to avoid such landfill sites. This involves difficulties, however, sincexe2x80x94as explained abovexe2x80x94reprocessing of the dusts in the metallurgical industry currently requires great effort, such as selection, and the dusts often have to be discharged in turn with waste gases.
The invention is based on the object of effectively reprocessing iron-containing residual smelting plant materials, in which iron may be present both in metallic form and in oxidic form, with lowest possible energy expenditure and with an expenditure on apparatus requiring only low investments, to be specific involving recovery of the iron contained in these residual smelting plant materials and wherever possible allowing technologies successfully proven in practice to be used. In particular, the intention is to avoid the dusts passing repeatedly through process stages provided one after the other in steel production and avoid them having an additional adverse effect on these stages.
This object is achieved according to the invention by the combination of following features:
residual smelting plant materials are processed into agglomerates,
the agglomerates are charged into an electric arc furnace,
melted and reduced,
and the resultant melt is refined.
It is of particular advantage if liquid and/or solid pig iron is additionally charged into the electric arc furnace and is likewise refined, the pig iron expediently being at least partially charged before the residual smelting plant materials. For energy-related reasons, the pig iron is charged in the liquid state. However, it may also be introduced in the form of ingots, either entirely or only in part. Part of the pig iron may also be substituted by scrap. There is also the possibility of substituting pig iron by a carburized liquid pool remaining from the residual melt. Carburizing may take place by adding lump and/or dust coal/coke.
With the method according to the invention, residual smelting plant materials can be successfully processed in large amounts. Residual smelting plant materials are advantageously charged in an amount of preferably approximately 40 to 50% of the total charge.
As the metal product, a crude steel, a semisteel or liquid pig iron can be produced.
However, in regular operation, i.e. with residual smelting plant materials occurring in normal amounts, refining is advantageously carried out up to a carbon content of at most 0.1%, i.e. the metal product is a crude steel.
The method according to the invention is also very well suited for processing rolling scale slurry, this advantageously having the oil removed beforehand, by treating with specific lime additives, such as calcined lime. This measure allows the oil contained in the rolling scale slurry to be chemically dispersed by CaO, before a hydration reaction with water occurs.
Dusts and/or slurries from converter and/or electric arc-furnace operation and/or the pig-iron production installation and/or the direct reduction installation are used in particular for charging as residual smelting plant material.
The residual smelting plant materials are advantageously mixed before charging and have calcined lime added as a binder, whereupon the residual smelting plant materials are agglomerated and the agglomerates are dried to a residual moisture content of less than 5%.
Preferably, first of all pig iron, preferably liquid pig iron, is charged into the electric arc furnace, whereupon the residual smelting plant materials are continuously charged over a predetermined time period and, during this time, the refining process is carried out, refining expediently taking place for a predetermined remaining time, for the vaporizing of zinc, without any charging of residual smelting materials being carried out.
An installation for carrying out the method according to the invention is designed as follows: with a mixing reactor, into which there opens at least one line feeding in residual smelting plant materials, an H2O feed line and a line feeding in binder, with an agglomerating device, preferably with a drying device, from which the dried agglomerates can be passed to a preferably provided screening device, with an electric arc furnace, into which there leads at least one line feeding in the agglomerates, preferably with a line passing the coarse fraction from the screening device into the electric arc furnace through at least one cover opening and/or a line passing the fine fraction to at least one lance protruding into the electric arc furnace, with a feed for pig iron leading into the electric arc furnace, a tapping opening for the slag and a tapping opening for the iron melt produced.
The installation preferably has a filter system, to which there leads a waste-gas line, extending from the arc furnace, and from which filter system a line for dusts separated from the waste gas leads to the mixing reactor, there expediently extending from the drying device a line carrying away vapours, which leads to the filter system.